This invention generally relates to mechanisms for steering powerboats and other watercraft.
Powerboats can be categorized in part in accordance with the design of their hulls. There are basically two kinds of hull designs for powerboats: displacement hulls and planing hulls. Displacement hulls are designed for vessels intended for cruising through water, while planing hulls are incorporated in boats designed to lift a part of the hull out of the water to skim the water surface. Planing boats are typically used in activities which require high boat speed, such as water-skiing and powerboat racing.
Powerboats also differ in the types of propulsion systems used. The powerhead can be mounted either inside the hull or outside the hull. In the latter case, the powerhead is mounted on the transom portion of the boat hull and is detachable. Another type of system, called a stern drive system, and sometimes referred to an inboard-outboard system, utilizes a powerhead mounted inside the hull of the boat with a portion of the drive unit extending through the transom. These systems create thrust through rotation of either a propeller or an impeller, which draws water from ahead and impels the water rearward to propel the boat forward.
In a conventional xe2x80x9cVxe2x80x9d type hull, the bottom of the boat terminates at the transom. In boats of this nature, either an outboard motor can be set on the transom or a stern drive, which has a motor within the boat directly in front of the transom and a drive shaft penetrating the transom, can be used to power the boat. In these types of boats, the driving force is produced (e.g., by a propeller or an impeller) behind and below the rearmost portion of the boat. In other hull constructions, the bottom of the central portion of the hull actually terminates forward of the transom so that there is a step between the bottom of the hull and the transom, forming a pocket in which, e.g., a jet propulsion unit can be mounted.
When boats of either of the above general types go from a rest or idle condition to a full-speed planing condition, they must accelerate through a condition which is known as xe2x80x9cgetting on planexe2x80x9d. When these boats are getting on plane, the angle of the boat in the water can be quite steep, which can hinder the visibility of the operator, as well as creating an inefficient running condition. Depending on the weight of the boat, the position of the load in the boat, and the power level of the engine, the condition of getting on plane can last an extended length of time. Once xe2x80x9con planexe2x80x9d, the angle of attack of the boat with respect to the water will level off and visibility is restored to the operator. The term xe2x80x9cplaning surfacexe2x80x9d, as used herein, refers to those portions of the hull surface which contact the water and support the weight of the boat when the boat is xe2x80x9con planexe2x80x9d, and specifically excludes stationary, generally vertical surfaces used to provide lateral stability and control, e.g., sidewalls of strakes or skegs, and movable, generally vertical surfaces used in steering, e.g., surfaces of rudders.
The steering systems for boats and watercraft vary widely in design and construction. On some single-propeller, inboard-engine powerboats, the shaft and propeller are fixed along the centerline of the hull, and the boat is steered using a vertical rudder blade pivoted on a post and located near the stern of the boat in close proximity to the propeller. Outboard and stern-drive boats, on the other hand, generally use directed-thrust steering to propel and the steer the boat through water.
In the case of a jet propulsion unit mounted to the hull and driven by an inboard motor, the jet propulsion unit intakes water through an opening in the bottom of the hull and discharges it through a thrust nozzle for propelling the watercraft and then through a pivotally supported steering nozzle for steering the watercraft. The steering nozzle directs the exiting water jet to one side or the other, thereby causing a steering rotation or yaw of the vessel which, in combination with the characteristics of the bottom surface of the hull, produces a turning maneuver.
Although the foregoing type of steering device is advantageous under normal running conditions, i.e., when there is sufficient thrust to overcome the momentum and directional drag of the vessel, at low speeds the jet propulsion unit does not develop significant thrust and the steering effectiveness is greatly reduced. Thus there is a need for a means of providing a positive turning force when a jet drive unit of a watercraft is turned off or operating at low rpm""s.
The present invention is directed to a watercraft having a hull with at least one turnable (i.e., pivotable) planing surface. In accordance with one preferred embodiment, the turnable planing surface is generally planar with at least one skeg or equivalent control surface projecting generally vertically downward from the planing surface. If two or more skegs are employed, these skegs are preferably parallel to each other. In a neutral position, the skegs are generally aligned with the centerline of the hull, causing no steering forces.
In accordance with another preferred embodiment, the turnable planing surface is a cylindrical section having a concave curved cross section, with opposing sides each having a strake-like structure. In a neutral position, the axis of the cylindrical section is generally aligned with the centerline of the hull, causing no steering force. In accordance with a more preferred embodiment, the turnable planing surface with strake-like sides is combined with at least one generally vertical, downwardly projecting skeg disposed between the strake-like sides.
Each of the above-described structures is designed to provide improved steering performance of watercraft, particularly jet-powered boats, while minimizing drag. Using a portion of the surface of the boat that is in contact with the water to provide the steering force improves the maneuverability of the boat.
In accordance with further preferred embodiments of the invention, a jet-powered watercraft is provided with a pair of skeg-bearing planing surfaces arranged along the centerline of the watercraft and turnable relative to that centerline. One turnable skeg-bearing planing surface is located in the foremost region of the area of the hull bottom which is wetted during planing and the other turnable skeg-bearing planing surface is mounted, either fixedly or pivotably, beneath the water jet propulsion unit. In one embodiment, the water jet propulsion unit is fixed (i.e., not turnable) and the skeg-bearing planing surface is turnable relative to the water jet propulsion unit. In another embodiment, the water jet propulsion unit is turnable relative to the hull centerline (e.g., in the manner of an outboard engine) and the skeg-bearing planing surface is fixed relative to the water jet propulsion unit (i.e., the skeg-bearing planing surface turns in unison with the water jet propulsion unit).
Preferably each turnable skeg-bearing planing surface comprises a bottom surface of a respective pivotable steering pad, with the area of the forward pad being less than the area of the rear pad. The front pad turns counter to the rear pad. The rear pad is designed to carry most of the boat weight at high speeds.
In accordance with another preferred embodiment of the invention, the front steering pad is provided mainly to enhance low-speed maneuverability. More specifically, means are provided for coupling the front steering pad to the steering wheel (and to the rear steering pad) only when the motor rpm""s are less than or equal to a predetermined threshold and then uncoupling the front steering pad from the steering wheel (and from the rear steering pad) when the motor rpm""s exceed the predetermined threshold.